FB41 and OB35 question

DzonasGotis

Member
Join Date
Apr 2007
Location
Vilnius
Posts
13
I'd like to know one more thing. If i need to uze PID as part of UNIT in one of my FB's. For example i have adresses: q0.0 - increase the heat of burner, q0.1 lower the heat of burner, q0.3 - start burner, i0.0 burner is on, PIW0 temperature meter, 90 degrees in celcius is the SP. Where i should put that data in FB41? If i call FB41 one of my FB does it still use the OB35 interupt?
 
Normally PID controller should be called at equal time intervals. One of means to achieve that is placeing the FB41 in OB35. But this is not obligatory.
 
Looking at your planned addresses, I don't think FB41 alone is the correct block to use in this application. I'd guess that FB42 might be more suitable. The parameters to attach your addresses to would be -

Q0.0 - increase the heat of burner - QLMNUP;
Q0.1 - lower the heat of burner - QLMNDN;
Q0.3 - start burner
I0.0 - burner is on
PIW0 - temperature meter - PV_PER;
90.0 - setpoint - SP_INT;

Alternatively FB41 + FB43 PULSE_GEN may be required depending on the type of actuators you are controlling. How are you increasing/decreasing the heat of the burner? Is there a motorised valve controlling gas flow? There's a lot more information required here.

Ken
 
Well it's a gas valve that increases or decreases the flow to the burner depending on the temperature that is in the dryer. And the only adreses that i have for this burner are: BurnerIsWorking IN, BurnerIsNotWorking IN, StartBurner OUT, IncreaseHeat OUT, DecreaseHeat OUT, VentilatorON IN, VentilatorON OUT. Ventilator is always running in the same speed, it turns on before the burnes and shuts down after the burner is shutdown. Maby anyone can suggest a smart example how should i sue PID in this situation. Of course i could write pid cycle just for this case but it'll take some time and i don't think it will be as accurate. Waiting for your replies!
 

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